% Listing 9-11 - Recursive zero finder
 function pt = findZeroAB(x)
% x is a lower-upper pair guaranteed to have
%                  y values of opposite sign
 y = fab(x);
 if abs(x(1)-x(2)) < .001
     pt = [x(1) y(1)];
 else
     mx = sum(x)/2;
     my = fab(mx);
     if my*y(1) < 0
         pt = findZeroAB([x(1) mx]);
     else
         pt = findZeroAB([mx x(2)]);
     end
 end
